Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$127.54	7.162%	$136.6744	$136.67	$136.65	$136.70
Purchase #2	$98.28	4.316%	$102.5218	$102.52	$102.50	$102.50
Purchase #3	$216.60	5.545%	$228.6105	$228.61	$228.60	$228.60
Purchase #4	$142.92	3.265%	$147.5863	$147.59	$147.60	$147.60
Purchase #5	$220.92	7.496%	$237.4802	$237.48	$237.50	$237.50
Purchase #6	$62.82	6.672%	$67.0114	$67.01	$67.00	$67.00
Purchase #7	$110.31	6.464%	$117.4404	$117.44	$117.45	$117.40
7 purchase totals =	$979.39		$1,037.3250	$1,037.32	$1,037.30	$1,037.30